1. Technical Field
The present invention relates to an image reading apparatus for reading images on an original.
2. Related Art
Reading devices such as a copy machine or a fax machine, or image reading devices such as a scanner for automatically reading image data from an original to input the data into a computer are widely used. In this kind of image reading devices, the light is irradiated onto the original from a light source, and the reflection light reflected from the original is received by an image sensor to read the image on the original. Recently, an image reading device capable of reading color images as well as monochrome images has been widely popularized. The image reading device for reading color images usually adopts a light source capable of emitting red, green, and blue (RGB) lights and an image sensor in which multiple pixel lines corresponding to each color are arranged in a vertical scanning direction. In addition, a color filter having a red, green, or blue color is provided in each pixel line (e.g., an on-chip filter).
However, the color filter installed in each pixel line often has a property of transmitting the light having a wavelength range other than that of a corresponding color, for example, a near infrared (IR) light. In this case, each pixel line is sensitive to the IR light as well as the red, green, and blue lights. As a result, the data read by each pixel line includes an IR light component as well as a desired color light component.
For this reason, a technique for inserting a reading filter for cutting out unnecessary wavelength lights such as an infrared light in the middle of an optical path for guiding the reflection light from the original to each pixel line has been proposed.
In addition, recently, due to increasing concern about security or electronization, a technique for forming an invisible image that cannot be recognized by human eyes on a special original, for example using an image forming medium (such as ink or toner) that absorbs or reflects the IR rays, is being adopted in order to distinguish the special original such as a note or a valuable paper from a typical original. In addition to the special original, for example, a technique for additionally forming an invisible image containing code information (such as an identification code) using the image forming medium on an original that has visible confidential information has been considered.
Therefore, it is necessary to provide an image reading apparatus capable of reading an infrared image in addition to a visible image.